This is a repository copy of Using knowledge anchors to facilitate user exploration of data graphs. White Rose Research Online URL for this paper: http://eprints.whiterose.ac.uk/141069/ Version: Accepted Version Article: Al-Tawil, M, Dimitrova, V orcid.org/0000-0002-7001-0891 and Thakker, D (2020) Using knowledge anchors to facilitate user exploration of data graphs. Semantic Web, 11 (2). pp. 205-234. ISSN 1570-0844 https://doi.org/10.3233/SW-190347 This article is protected by copyright. This is an author produced version of a paper published in Semantic Web. Uploaded in accordance with the publisher's self-archiving policy. Reuse Items deposited in White Rose Research Online are protected by copyright, with all rights reserved unless indicated otherwise. They may be downloaded and/or printed for private study, or other acts as permitted by national copyright laws. The publisher or other rights holders may allow further reproduction and re-use of the full text version. This is indicated by the licence information on the White Rose Research Online record for the item. Takedown If you consider content in White Rose Research Online to be in breach of UK law, please notify us by emailing [email protected] including the URL of the record and the reason for the withdrawal request. [email protected] https://eprints.whiterose.ac.uk/ Using Knowledge Anchors to Facilitate User Exploration of Data Graphs Editor(s): Krzysztof Janowicz, University of California, USA Solicited review(s): Valentina Maccatrozzo, Vrije Universiteit Amsterdam, Netherlands; Bo Yan, University of California, USA; Simon Scheider, Utrecht University, Netherlands. Marwan Al-Tawila,b,*, Vania Dimitrovab, Dhavalkumar Thakkerc,b a King Abdullah II School of Information Technology, University of Jordan, Amman, Jordan b School of Computing, University of Leeds, Leeds, UK c Faculty of Engineering and Informatics, University of Bradford, Bradford, UK Abstract. This paper investigates how to facilitate users’ exploration through data graphs. The prime focus is on knowledge utility, i.e. increasing a user’s domain knowledge while exploring a data graph, which is crucial in the vast number of user-facing semantic web applications where the users are not experts in the domain. We introduce a highly unique exploration support mechanism underpinned by the subsumption theory for meaningful learning. A core algorithmic component for operationalising the subsumption theory for meaningful learning is the automatic identification of knowledge anchors in a data graph (KADG). We present several metrics for identifying KADG which are evaluated against familiar concepts in human cognitive structures. The second key component is a subsumption algorithm that utilises KADG for generating exploration paths for knowledge ex- pansion. The implementation of the algorithm is applied in the context of a Semantic data browser in a music domain. The resultant exploration paths are evaluated in a task-driven experimental user study compared to free data graph exploration. The findings show that exploration paths, based on subsumption and using knowledge anchors, lead to significantly higher increase in the users’ conceptual knowledge and better usability than free exploration of data graphs. The work opens a new avenue in semantic data exploration which investigates the link between learning and knowledge exploration. We provide the first frame- work that adopts educational theories to inform data graph exploration for knowledge expansion which extends the value of exploration and enables broader applications of data graphs in systems where the end users are not experts in the specific domain. Keywords: Data graphs, knowledge utility, data exploration, meaningful learning, knowledge anchors, exploration paths. 1. Introduction tasks) to browsing through large information spaces with many options (like exploring job opportunities, In recent years, RDF linked data graphs have be- travel and accommodation offers, videos, music). Of- come widely available on the Web and are being ten, the users have no (or limited) familiarity with the adopted in a range of user-facing applications offering specific domain. When users are novices to a domain, search and exploration tasks. In contrast to regular their cognitive structures about that domain are un- search where the user has a specific need in mind and likely to match the complex knowledge structures of a an idea of the expected search result [1], exploratory data graph that represents the domain. This can have search is open-ended requiring significant amount of a negative impact on the exploration experience and exploration [2], has an unclear information need [3], effectiveness, as users may be unable to formulate ap- and is used to conduct learning and investigative tasks propriate knowledge retrieval queries (users do not [4]. There are numerous examples from exploring re- know what they do not know [3]). Moreover, users can sources in a new domain (like in academic research face an overwhelming amount of exploration options *Corresponding author (E-mail: [email protected]). and may not be able to identify which exploration work showed that when exploring data graphs in un- paths are most useful; this can lead to confusion, high familiar or partially familiar domains, users serendip- cognitive load, frustration and feeling of being lost. itously learn new things that they are unaware of [17– To overcome these challenges, appropriate ways to 19]. However, not all exploration paths can be benefi- facilitate users’ exploration through data graphs are re- cial for knowledge expansion: paths may not bring quired. Research on exploration of data graphs has new knowledge to the user leading to boredom, or may come a long way from initial works on presenting bring too many unfamiliar things so that the user be- linked data in visual or textual forms [5,6]. Recent comes confused and overwhelmed [18]. studies on data graph exploration have brought to- The key contribution of this paper is a novel com- gether research from related areas - Semantic Web, putational approach for generating exploration paths personalisation, adaptive hypermedia, and human- that can lead to expanding users’ domain knowledge. computer interaction - with the aim of reducing users’ Our approach operationalises Ausbel’s subsumption cognitive load and providing support for knowledge theory for meaningful learning [20] which postulates exploration and discovery [7–9]. Several attempts that human cognitive structures are hierarchically or- have developed support for layman users, i.e. novices ganised with respect to levels of abstraction, general- in the domain. Examples include: personalising the ity, and inclusiveness of concepts; hence, familiar and exploration path tailored to the user’s interests [10], inclusive entities are used as knowledge anchors to presenting RDF patterns to give an overview of the subsume new knowledge. Consequently, our approach domain [11], or providing graph visualisations to sup- to generate exploration paths includes: port navigation [12]. However, existing work on facil- computational methods for identifying knowledge itating users’ exploration through data graphs has ad- anchors in a data graph (KADG); and dressed mainly investigative tasks, omitting important algorithms for generating exploration paths by uti- exploratory search tasks linked to supporting learning. lising the identified knowledge anchors. The exploration of a data graph (if properly as- To find possible knowledge anchors in a data graph, sisted) can lead to an increase in the user’s knowledge. we utilise Rosch’s notion of Basic Level Objects This is similar to learning through search - an emerg- (BLO) [21]. According to this notion, familiar cate- ing research area in information retrieval [13,14], gory objects (e.g. the musical instrument Guitar) are which argues that “searching for data on the Web at a level of abstraction called the basic level where should be considered an area in its own right for future the category’s members (e.g. Folk Guitar, Clas- research in the context of search as a learning activity” sical Guitar) share attributes (e.g. both have a [15]. In the context of data graphs, learning while neck and a bridge) that are not shared by members (e.g. searching/exploring has not been studied. The closest Grand Piano, Upright Piano) of another cat- to learning is research on tools for exploration of in- egory at the same level of abstraction such as . terlinked open educational resources [16]. However, Piano We have adapted metrics from formal concept analy- this is a very specific context, and does not consider sis for detecting knowledge anchors in data graphs. the generic context of learning while exploring data The KADG metrics are applied on an existing data graphs in any domain. This generic learning context is graph, and the output is evaluated against human Basic addressed here. Level Objects in a Data Graph (BLODG) derived via The work presented in this paper opens a new ave- free-naming tasks. nue that studies learning through data graph explora- To generate exploration paths, we first identify the tion. It addresses a key challenge: how to support peo- closest knowledge anchor to be used as a starting ple who are not domain experts to explore data graphs point, from where we use subsumption to find a set of in a way that can lead to expanding their domain transition narratives to form a path that can expand the knowledge. We investigate how to build automated user’s knowledge. The effectiveness of our novel ex- ways for navigating through data graphs in order to ploration approach is evaluated in a study with a Se- add a new value to the exploration, which we call mantic data browser in the Music domain. Subsump- ‘knowledge utility’ - expanding one’s domain tion-based exploration paths are compared to free data knowledge while exploring a data graph1. Our earlier graph exploration. The results show that when users 1 We follow definitions of utility (i.e. reducing users’ cognitive load in knowledge retrieval) and usability (i.e.